"Stickies" have long been identified as a troublesome contaminant in the manufacture of paper using secondary or recycled fibre as an ingredient. Stickies are, as the name suggests, tacky regions present in the paper product being formed. Typical stickies are non-hardening glues, such as those used on packaging tapes, on price labels, masking tape, office or other stationery, adhesive or any other application where quick tacking properties are required.
The contaminants that form the stickies enter the paper-making process with secondary fibre sources, i.e., recycled paper products. When recycled paper on which glue had been applied is defibred, the glues will form particulate contaminants. The surface of these particles remains adhesive after they have been retained on the surface of the paper being made. The adhesive surface of these stickies can cause problems by picking up debris in the furnish such as ink, sand or fibre particles.
In a typical papermaking operation, a pulp slurry containing about 2 to 3% of fibre in water is subjected to various filtration, drying, callendering, surface coating, reeling and winding steps.
An industry where stickies are especially troublesome is the boxboard making industry. Boxboard is used for making boxes for consumer products such as detergent boxes, etc. Often the one surface of the boxboard, known as the topliner, is made of a whiter grade of paper than the other surface, known as the backliner. This topliner is also often coated (usually with clay) in order to impart a white smooth surface suitable for printing.
The presence of stickies is often made apparent during the unwinding of the boxboard rolls just prior to printing and converting them to boxes.
When stickies are present in the backliner two problems may occur:
(1) Some of the stickies from the backliner may transfer to the topliner or coated topliner. This causes a visible blemish on the surface to be printed, which is unacceptable. Furthermore, the adhesive material may be transferred from the paper surface onto the printing press, subsequently causing a blemish on the paper surface with each application of the press to the paper surface.
When this occurs, it is necessary to stop production and to clean the printing press. Often the paper supplier is required to pay for the lost production and the cost of cleaning the printing press.
(2) Particles from the topliner, or the clay coating the topliner, may be transferred to the backliner during the unwinding of the paper rolls because they stick to the tacky surface of the stickies present on the backliner. The surface defects caused by this phenomenon are often referred to in the trade as "hickies". The printed product containing hickies is unacceptable from a packaging and marketing standpoint and is rejected for end use. Often this board and the associated lost printing time are charged to the boxboard manufacturer.